Large-screen, high-brightness electronic projection display apparatuses serve different broad areas of application such as e.g. electronic presentations for business, education, advertising, entertainment, simulation and status and information.
In order to fulfil the high brightness requirements of the present projection systems, a light source with a high level of power is needed. This often prevents formation of a compact projection display apparatus.
In projection systems, typically lamps having a power of 250 W are used. Increase of the luminous flux can either be performed by raising the power level of the lamp without changing the internal structure of the lamp, which leads to fast deterioration of the lamp such that the lifetime of the lamp is significantly shortened, or by changing the internal structure of the lamp, i.e. increasing the length of the luminous element, which leads to a significant increase of the size of the lamp, thereby limiting the compactness of the projection system. None of these solutions allows to obtain a compact and durable projection system.
In European Patent Application EP0683425 A1, a multiple lamp solution for projection systems is described. In the application, a projection system is described having two or more lamps, a light transmitting optical system, a light valve and a projection lens. The lamps are arranged side by side and allow a more compact system. In a specific embodiment, the light transmitting optical system comprises multiple sets of lens arrays as optical integrators. The image from the lens arrays is focused on the light valve by way of an additional lens. Adjacent to the lamps, UV/IR filters are positioned to remove ultraviolet (UV) and/or infrared (IR) radiation out of the light path. Nevertheless, reflection of IR radiation back into the lamps leads to an increased deterioration of the lamps.
Furthermore, today's projection systems also suffer from lack of compactness of the projection systems as a whole. They also still do not allow an optimal illumination of the light valve, i.e. combining an optimum light output of the light sources onto the light valve with a reduction of the heat load of the light valve.